Base station equipment and a method for steering an antenna beam

ABSTRACT

A method for steering an antenna beam and base station equipment including at least one antenna array having a plurality of elements and at least one channel unit having a means for phasing a signal to be transmitted and received by the antenna array such that gain from the antenna array is the greatest in the desired direction. In order to improve the spectral efficiency of the system, the channel unit includes a means for searching for the incoming directions and delays of the received signal components and a means for controlling the phasing means of the opposite transmission direction based on the information.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a base station equipment for receiving andtransmitting a signal of a desired user, in which the signal to bereceived may arrive at the equipment along a plurality of paths with aplurality of delays.

2. Description of Related Art

The present invention is applicable for use in a data transmissionsystem applying any multiple access method, but especially in a cellularsystem using code division multiple access. Code division multipleaccess (CDMA) is a multiple access method, which is based on the spreadspectrum technique and which has been applied recently in cellular radiosystems, in addition to the prior FDMA and TDMA methods. CDMA hasseveral advantages over the prior methods, for example, spectralefficiency and the simplicity of frequency planning. An example of aknown CDMA system is the broadband cellular radio standard, EIA/TIAIS-95.

In the CDMA method, the narrow-band data signal of the user ismultiplied to a relatively wide band by a spreading code having aconsiderably broader band than the data signal. In known test systems,bandwidths, such as 1.25 MHz, 10 MHz, and 25 MHz have been used. Inconnection with multiplying, the data signal spreads to the entire bandto be used. All users transmit by using the same frequency bandsimultaneously. A separate spreading code is used over each connectionbetween a base station and a mobile station, and the signals of thedifferent users can be distinguished from one another in the receiverson the basis of the spreading code of each user.

Matched filters provided in the receivers are synchronized with adesired signal, recognized based on a spreading code. The data signal isrestored in the receiver to the original band by multiplying it again bythe same spreading code that was used during the transmission. Signalsmultiplied by some other spreading code do not correlate in an idealcase and are not restored to the narrow band. These signals appear asnoise with respect to the desired signal. The spreading codes of thesystem are preferably selected such that they are mutually orthogonal,i.e., they do not correlate with each other.

In a typical mobile phone environment, the signals between a basestation and a mobile station propagate along several paths between thetransmitter and the receiver. This multipath propagation is mainly dueto the reflections of the signal on the surrounding surfaces. Signalswhich have propagated along different paths arrive at the receiver atdifferent times due to their different transmission delays. In the CDMA,the multipath propagation can be exploited during the reception of thesignal in the same way as diversity. The receiver generally used in aCDMA system is a multibranch receiver structure where each branch issynchronized with a signal component which has propagated along anindividual path. Each branch is an independent receiver element, thefunction of which is to compose and demodulate one received signalcomponent. In a conventional CDMA receiver, the signals of the differentreceiver elements are combined advantageously, either coherently orincoherently, whereby a signal of good quality is achieved.

CDMA systems can also apply a soft handover wherein a mobile station maysimultaneously communicate with several base stations by utilizingmacrodiversity. The connection quality of the mobile station thusremains high during the handover and the user does not notice a break inthe connection.

Interference caused by other connections in the desired connectionappears in the receiver as noise that is evenly distributed. This isalso true when a signal is examined in an angular domain according tothe incoming directions of the signals detected in the receivers. Theinterference caused by the other connections in the desired connectionalso appears in the receiver as distributed in the angular domain, i.e.,the interference is rather evenly distributed into the differentincoming directions.

The capacity of the CDMA, which can be measured by spectral efficiency,has been further improved with sectorization. A cell is then dividedinto sectors of a desired size that are serviced by directionalantennas. The mutual noise level caused by the mobile stations can thusbe reduced significantly in the base station receiver. This is based onthe fact that, on average, the interference is evenly distributedbetween the different incoming directions, the number of which arereduced by sectorization. The sectorization can naturally be implementedin both transmission directions. The advantage provided in the capacityby the sectorization is proportional to the number of the sectors.

A sectorized cell may also use a special form of soft handover, a softerhandover, wherein a mobile station performs a handover from one sectorto another by communicating simultaneously with both sectors. Eventhough soft handover improves the connection quality and sectorizationincreases the system capacity, the movement of the mobile stationsnaturally leads to the stations performing several handovers from onesector to another. This loads the processing capacity of the basestation controller. Several soft handovers also produce a situationwhere several mobile stations communicate simultaneously with more thanone (usually two) sector, whereby the increased capacity provided by thesectorization is lost as a signal of a mobile station is audible in awide sector.

The multiple access interference of the CDMA systems has also beenreduced by different known multiple access interference cancellation(IC) methods and multi-user detection (MUD). These methods are bestsuited for reducing the interference produced within the user's owncell, and the system capacity can be increased to about double comparedto a system implemented without interference cancellation. However,these methods do not significantly improve the size of the coverage areaof the base station compared to known technology. Also, the IC/MUDtechniques are complicated to realize, wherefore they have mainly beendeveloped in the uplink direction.

Another method that has been developed is an SDMA (Space DivisionMultiple Access) method wherein the users are distinguished from oneanother based on their location. This is performed in such a way thatthe beams of the receiver antennas at the base station are adjusted tothe desired directions according to the location of the mobile stations.For this purpose, the system uses adaptive antenna arrays, i.e., phasedantennas, and the processing of the received signal, by which the mobilestations are tracked.

The use of the SDMA in connection with the CDMA provides severaladvantages over the prior methods, such as sectorization. If the sectorbeams in the sectorization are narrowed in order to increase thespectral efficiency, the number of the handovers to be performed fromone sector to another also increases. This in turn increases too muchthe calculation capacity required in the base station controller.

In connection with the application of the SDMA, the background art isillustrated in A. F. Naguib, A. Paulraj: Performance of CDMA CellularNetworks With Base-Station Antenna Arrays (Proc. International ZurichSeminar on Digital Communications, pp. 87-100, Zurich, Switzerland,March 1994), which is incorporated herein by reference. In the SDMA, asignal is received by an antenna array, and the received signal isshaped by digital signal processing in such way that the directivitypatterns of the antennas are suitable for the stages following theshaping in the receiver. In prior art arrangements, the received signalis shaped in order to maximize the signal-to-interference ratio of thedesired signal. The received signal is thus shaped such that thedirectivity pattern of the antenna array minimizes the interferencecaused by the other connections in the desired signal. In thearrangement according to the aforementioned reference, each detectedsignal component is subjected to individual beam shaping, i.e., theimpulse response must be known before the shaping.

Experimental Studies of Space-Division-Multiple-Access Schemes forSpectral Efficient Wireless Communications by G. Xu, H. Liu, W. J.Vogel, H. P. Lin, S. S. Jeng and G .W. Torrence (IEEE Int. Conf. OnComm. ICC 1994, New Orleans, USA, IEEE 1994), which is incorporatedherein by reference, discloses a method which applies the SDMA and inwhich the directivity pattern of the transmitter antennas is shaped.However, the method disclosed is suitable for use only in systems whereboth transmission directions are on the same frequency.

SUMMARY OF THE INVENTION

The purpose of the present invention is to realize a base stationequipment and a method for steering transmission antennas, by which thespectral efficiency can be improved further compared to the prior CDMAsystems, so that the technical implementation of the equipment willstill be advantageous and wherein a connection of good quality can bemaintained between a base station and a mobile station even in difficultpropagation conditions of radiowaves. The purpose of the invention is toapply the SDMA efficiently in a CDMA environment by utilizing new typeof multidimensional search and the connection quality informationtransmitted by a mobile station. The application of the invention doesnot require both of the transmission directions to be on the samefrequency.

This is achieved with a base station equipment of the present inventionin which the channel unit includes means for searching for the incomingdirections and delays of the received signal components, and means forcontrolling the phasing means of the opposite transmission directionbased on the information.

The invention also relates to a method for steering an antenna beam in abase station equipment, in which method a signal is received andtransmitted by an antenna array consisting of several elements byphasing the signal to be received and transmitted such that the gainfrom the antenna array is the greatest in the desired directions In themethod according to the invention, in that in the base stationequipment, the incoming directions and delays of the signal componentsreceived from the mobile station are searched for, and the phasing ofthe signal to be transmitted in the opposite transmission direction iscontrolled based measurement.

The method according to the invention provides considerably betterspectral efficiency when compared to the conventional cellular systems,including systems applying the CDMA method. The method increases boththe number of the channels used by a factor of 10 to 100, and the sizeof the coverage area of the base station by a factor of 5 to 10. This isbased on that fact that the interference to the other users decreasessignificantly in the downlink transmission direction, when the signal issteered during the transmission in the directions from which the signalcomponents from the mobile station were received advantageously at thebase station.

According a the first preferred embodiment of the invention, the signalprocessing can be performed digitally on the base band, whereupon theantenna beams can be steered directly to the desired directions byphasing the received signal. In a second preferred embodiment of theinvention, the signal phasing is performed analogically, thus resultingin a number of fixed antenna beams from which the beams receiving thebest components of the desired signal are selected for the reception.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the preferred embodiments of the invention will bedescribed in greater detail with reference to the examples according tothe accompanying drawings, in which

FIG. 1 illustrates the multipath propagation of a signal between amobile station and a base station;

FIG. 2a illustrates, on a time domain, the scattering caused by themultipath propagation of a signal;

FIG. 2b illustrates, on the angle-of-arrival domain, the scatteringcaused by the multipath propagation of a signal;

FIG. 3 illustrates a possibility of steering the beam of the basestation antennas towards the mobile station;

FIG. 4 shows a possible implementation of an adaptive antenna array;

FIG. 5 is a block diagram illustrating a possible structure of anequipment according to the invention;

FIGS. 6a and 6b are block diagrams illustrating two examples of thestructure of an individual channel element;

FIG. 7 is a block diagram illustrating another possible example of theequipment according to the invention;

FIGS. 8a and 8b illustrate two examples of the alternative structure ofan individual channel element; and

FIG. 9 illustrates more closely an example of the structure of anindividual channel element.

DETAILED DESCRIPTION OF THE CURRENTLY PREFERRED EMBODIMENT OF THEINVENTION

In the following, the method and equipment according to the inventionwill be described in greater detail using the CDMA system as an example,but not restricting the description thereto, however, since theinvention is also applicable in connection with other multiple accessmethods, as will be evident for a person skilled in the art on the basisof the description below.

FIG. 1 illustrates the typical multipath propagation of a transmittedsignal in a cellular system. The figure shows a base station 100 and amobile subscriber equipment 102 communicating with the base station. Acharacteristic feature of cellular radio systems is that the mobilestations are surrounded by surfaces that reflect and scatter radiowaves.Such surfaces may be, for example, buildings and walls formed by thenature, such as mountains and hills. Mobile stations typically transmitwith an omnidirectional antenna pattern. The figure illustrates a fewrays 112, 114, 116 originating from a mobile station. The surfaces 104,108 situated close to the mobile station 102 reflect the transmittedsignal, which therefore arrives at the antenna of the base station 100along several different paths, but the delay between the differentsignal components is rather small. The reflecting surfaces situatedfurther away, in the figure reference 106, such as larger buildings andmountains, produce signal components 114 which arrive at the basestation 100 several, even dozens of microseconds later. There may alsobe obstacles 110 in the terrain that prevent a direct connection betweenthe mobile station and the base station.

FIG. 2a illustrates, on the time domain, an example of a momentary delayof signal components caused by the multipath propagation of the signalat a base station receiver. The horizontal axis 200 of the schematicfigure shows the time and the vertical axis 202 shows the power of thereceived signal. In the example of FIG. 2a, the base station receiverhas detected three groups of signal components 204, 206, 208 which havearrived at the receiver at different times and among which the component208 is significantly more delayed than the others.

As the example of FIG. 1 shows, the different signal components arrivenot only at different times, but also from different directions. Thesignal scatters not only in the time domain, but also in the angulardomain, which can be described by the angle of arrival (AoA) of thesignal. FIG. 2b illustrates an example of a momentary scattering as afunction of the angle of arrival, caused by the multipath propagation ofthe signal, at the base station receiver. The vertical axis 202 of FIG.2b shows the power of the received signal component, and the horizontalaxis 210 shows the angle of arrival. In the example of FIG. 2b, thesignal components 212, 214 arrive from two directions.

In large cells, so-called macrocells, wherein the base station antennasare situated high, the signal components generally arrive at the antennawith only a few different angles of arrival, which are usually at thevicinity of the direct ray between the mobile station and the basestation. In small microcells where the base station antennas are usuallysituated below the roofs of buildings, the angles of arrival of thesignal components are found to show far greater dispersion, since in thesame way as the mobile stations, the base stations are often surroundedby several reflecting surfaces situated near by.

The multipath propagation has been described above in the uplinktransmission direction. It is naturally clear that a correspondingphenomenon also occurs in the opposite downlink direction. It can alsobe stated that the multipath routes are mainly symmetrical in bothdirections, since the scattering and reflection are not greatlydependent on the frequency. However, it should be noted that fast signalfadings are mutually independent in different transmission directions.Therefore, if the base station detects a signal component that hasarrived from the mobile station at the angle of arrival of α₀,transmitting a signal with the same angle α₀ guides the signal in thedirection of the mobile station, except for fast fadings.

Based on the above, the multipath propagating environment typical ofcellular systems leads to the reception of a signal in the base stationswhich is distributed in time into several components that are delayeddifferently and in the angular domain into components arriving fromseveral different directions. Both distribution profiles vary in timesince the subscriber equipments move, but the variation is rather slow,i.e., in the range of a few seconds, and the profiles can besynchronized with and they can be monitored.

The received signal components are thus characterized by themultidimensionality of the type described above that is illustratedabove with the time-angular domain, i.e., (α, τ) domain, and that can beutilized in the base station according to the invention for improvingthe detection of the signal to be received. In the method according tothe invention, the best signal components of the received signal aresearched for in the multidimensional signal domain, the receiver beingcontrolled by the components such that the detected components can bepreferably combined and detected. The most simple standard for thesignal quality can be the received power level, but also other standardscan be used, for example the signal-to-noise ratio.

The equipment according to the invention utilizes an adaptive antennaarray, which is an antenna array consisting of several differentelements. FIG. 4 illustrates a possible implementation of an adaptiveantenna array, which can be applied in connection with the firstpreferred embodiment of the invention. The antenna array comprises Lantenna elements 400, 402, 404, which may be, for example,omnidirectional antennas.

Each antenna element is connected to radio-frequency parts 406, 408,410, which convert the received signal into an intermediate frequencyand sample the signal into (I,Q) components according to knowntechnology. The obtained complex samples are then multiplied by thecorresponding complex weighting coefficients w_(i), wherein i=1, . . . ,L, in multipliers 412, 414, 416. The samples 422, 424, 426 that havethus been multiplied are applied via an adder 418 to other parts of thereceiver.

The complex weighting coefficients w_(i) are selected according to analgorithm, which is usually adaptive, such that an antenna pattern ofthe desired shape is achieved. This manner of shaping the receivedsignal can be called digital phasing of the signal, since it isperformed on a signal digitized on the base band, but due to thisshaping the received signal antenna gain can be oriented in the desireddirections. An antenna array as such may comprise either directional oromnidirectional antenna elements. Phasing the signal obtained from thedifferent antennas and combining the phased signals produces kind ofvirtual antenna beams into the desired directions. A correspondingtreatment can also be performed on the signal to be transmitted, wherebya desired radiation pattern can be achieved.

FIG. 3 illustrates how an antenna array consisting of an evenly spacedlinear group comprising four elements 300, 302, 304, 306 produces astrong directed beam 310 with the angle of arrival of α towards a mobilestation 308. A group of smaller side beams 312 to 316 are also formed.This directivity can thus be implemented with the signal phasing withoutthe antennas as such being directional.

In the arrangement according to the invention, the multiple accessinterference of the receiver is reduced with antenna beams that aredirected in the angular domain and that are produced by means of a newtype of receiver applying time-angle diversity. In the arrangementaccording to the invention, the angles of arrival measured from thereceived signal can also be used in the transmission direction, wherebythe connection quality is improved in both transmission directions.

In the following, a first preferred embodiment of the invention, whichrelates to applying the digital phasing of the signal in the CDMAsystem, will be described first.

The receiver applying time-angle diversity used at the base stationcomprises digital receiver means that can monitor the received signalcomponents in the two-dimensional (α, τ) domain and demodulate thedesired signal components. Before the demodulation, the receiveddigitized signal samples are subjected to phasing by means of which theantenna gain of the received signal is oriented in the desired signalincoming directions.

In the preferred embodiment, the antenna beams produced by the phasingare beams having a predetermined shape that is determined by theweighting coefficients w_(i) and the antenna geometry. Thesecoefficients can easily be calculated for each angle of the greatestgain if the shape of the antenna beam as such remains constant.Therefore, the phasing can be adjusted rapidly since it is onlydependent on one parameter, i.e., the angle of arrival α.

In the method according to the invention, there is no need to applyknown complicated techniques, such as MUSIC, for estimating the angle ofarrival or adaptive algorithms, such as LMS and DMI. Even though thesealgorithms enable the calculation of the optimal beam shape for thesignal to be received, so that the signal-to-noise ratio of the desiredsignal can be maximized by directing the zero points of the antennapattern towards the sources of interference, this is not necessary inconnection with the CDMA since, as described above, in the CDMA theinterference signal is distributed to resemble noise without having anyclear directions of interference source. Therefore, it is sufficient inan environment with evenly distributed interference that the angles ofthe greatest gain of the antenna beams having a predetermined shape arepointed in the directions from which the best signal components arereceived. This enables the implementation of a more simple receivercompared to the prior art.

In the method according to the invention, the receiver thus searches forthe desired signal components in the (α, τ) domain. This is performed bycross-correlating the received spread-spectrum signal with the desiredspreading code and by comparing the obtained measurement results withthe threshold values given. The search can be understood as a sweep ofan antenna beam over the given area, simultaneously performing themeasurement of the channel impulse response and the collection of thesignal energy of the terminal equipments received from each direction.The receiver thus detects the direction and code phase of the receptionof the best signals and allocates a required number of demodulationmeans for synchronizing with and receiving these signal components. Thereceived demodulated signal components can be preferably combined in thereceiver. The search for the best signal components is performedcontinuously and the allocation of the demodulation means is changed, ifnecessary.

The receiver thus knows at all times the directions from which the bestsignal components from the mobile stations are received. Thisinformation can also be used in the base station equipment according tothe invention in the downlink direction. This may be performed, forexample, such that the controller of the transmitter-receiver informsthe transmitter unit of the directions where significant signalcomponents have been detected. The transmitter unit may phase the signalto be transmitted with the adaptive antenna array in such a way that theangles of the greatest gain of the antenna beams point in the desireddirections. There may be one or more transmission beams and their numbermay also differ from the number of the receiver beams.

This method provides considerable interference cancellation also in thedownlink direction. The antenna array used in the transmission may bethe same as the antenna array used in the reception. It may also be aseparate antenna array. The signal phasing is performed in the same wayas during the reception with the weighting coefficients.

In the arrangement according to the invention, it is also possible touse the delays of the measured signal components such that the signalcomponents to be transmitted are deliberately delayed with respect toeach other so that the terminal equipment receives the componentspreferably with a time difference that is longer than one bit of aspreading code, i.e., a chip. In such a case, a conventional rakereceiver can distinguish the received signals from one another and toutilize multipath diversity.

In environments with great delay spreads, the arrangement according tothe invention can be used to compensate for the mutual delays ofcomponents that propagate along different paths by providing thecomponents with mutual delay differences during the transmission, sothat it is easier for the terminal equipment to measure the impulseresponse. This is based on that fact that since the delay spread can bedecreased with the method according to the invention in a signalreceived by the terminal equipment, the size of the measurement windowof the impulse response in the terminal equipment can be correspondinglyreduced, whereupon a better estimate of the channel is obtained.

The arrangement according to the invention may use, for example, priorart mobile stations, which continuously perform measurements on theconnection quality from the signal they have received from the basestation. This information may comprise data concerning the number of thesignal components the mobile station has received. The arrangementaccording to the invention may utilize the results of the connectionquality measurements performed by the mobile station when the beams ofthe transmission antennas are directed in the downlink direction.

The mobile station transmits the measurement results it has collected tothe base station. On the basis of the information received from themobile station and the measurements it has performed itself, the basestation may vary the number, shape or direction of the antenna beams ituses for the transmission of the signal intended to the mobile station.These changes can be implemented gradually, so that the mobile stationcan follow the changing signal.

The base station may also use the connection quality information it hasreceived from the mobile station for adjusting the transmit power ofeach antenna beam if the measurement results show that theaforementioned measures do not improve the signal quality in the mobilestation.

One advantage of the method described above is that for example in adifficult fading situation the mobile station may transmit to the basestation a request to change the parameters of the antenna beams used inthe signal transmission, for example, the direction, shape and number,whereby the quality of the signal received by the mobile station can beimproved rapidly.

The prior art CDMA systems use a pilot signal that is transmitted byeach base station and that is is used in the identification of basestations, in power measurement and for enabling coherent reception in amobile station. In known systems, a pilot signal that is adata-unmodulated spreading-coded signal is transmitted to the coveragearea of the base station in the same way as the actual traffic channels.

A CDMA system implemented in the manner according to the invention mayapply such a method for transmitting a pilot signal that uses antennabeams changing in time in the transmission and reception of datasignals. It is then possible to transmit a first pilot signal in atransmission direction that is constant in time, and second pilotsignals in transmission directions that change in time and that maycorrespond to the transmission directions used in the transmission ofthe data signals.

Therefore, a pilot signal provided with transmission directions thatremain constant in time can be used for the detection of a base stationand for power measurements for detecting a need for a handover. Sincethe antenna directivity pattern used differs from the pattern of thedata signals, the signal cannot be used as a reference for coherentdetection. It is possible to use for this purpose a pilot signal that istransmitted with the same antenna pattern in connection with each datasignal and that therefore propagates along the same path as the actualdata signal and that enables coherent detection in mobile stations.

In the arrangement according to the invention, a pilot signal canfurther be transmitted using a relatively narrow antenna beam, and theangle of the greatest gain of this antenna beam can be directed in sucha way that the antenna beam sweeps the cell area. Thus the antenna beamcomprising the pilot signal sweeps the cell like a lighthouse, and thetransmission of a continuous pilot to the entire cell area can beavoided. The pilot can also be transmitted with several sweeping antennabeams, which are phased such that they do not overlap. The base stationinforms the mobile stations on a control channel about the time when thepilot channel sweeps each area.

In the following, the structure of an equipment according to the firstembodiment of the invention will be described. FIG. 5 is a block diagramillustrating the structure of an equipment according to the invention.The equipment comprises an antenna array 500 consisting of L separateantenna elements. The antenna array may be linear, planar(two-dimensional) or omnidirectional. The antenna array 500 receives amultipath-propagated signal that is delayed in different ways fromseveral different directions from each mobile station with each of the Lelements, performs the preamplification, converts the signal into anintermediate frequency and digitizes all the L signals. The obtained Ldigital complex I,Q samples 514 are supplied into an input of channelelements 504, 506, 508.

Each active mobile station communicating with the base station isserviced by one channel element, which performs digital signalprocessing both on the received signal and on the signal to betransmitted, as will be described in greater detail below. Each channelelement comprises a (α, τ) receiver and a corresponding transmitter. Thedigital shaping functions of the antenna beam, realized by means of thesignal phasing, are performed in a channel element both in thetransmission direction and in the direction of reception.

In the direction of reception, a channel element filters the signal onthe angle-space domain, demodulates the received signal components andcombines them in a diversity combiner and in the end decodes the signalthat has been received from the mobile station and that has beencombined. The obtained user data bits are supplied further to a basebandunit 510, which forwards them to other parts of the network.

In the transmission direction, the user data bits arrive from the otherparts of the network to the baseband unit 510, which forwards them tothe correct channel element 504 to 508 where they are encoded, modulatedby a spreading code and subjected to the phasing of the signal to betransmitted, the phasing determining the directions of the antenna beamsto be transmitted. The obtained L signals are supplied to each of the Lelements of the antenna array 502. In practice, the reception andtransmission antenna arrays 500, 502 may be either separate orimplemented by the same physical antenna array where the directions oftransmission and reception are separated with suitable duplexfiltration.

In the transmission antenna array 502, the signals that have arrivedfrom each channel element and that are intended to each antenna elementare converted into analog form, transferred to a radio frequency andtransmitted via the antenna elements.

In the arrangement according to the invention, the transmission andreception antenna arrays may naturally comprise a different number ofantenna elements, even though the description above discloses the samenumber L of elements in each group for the sake of simplicity. Thefigure also shows a control block 512, which controls the operation ofthe different units of the equipment, such as the allocation of thechannel units to different connections according to the messages fromthe base station controller.

FIG. 6a is a block diagram illustrating the structure of a channelelement in the equipment according to the first embodiment of theinvention. The channel element comprises one or several digital receiverunits 600, 602 two of which are shown in the figure, one or severalsearcher units 604 one of which is shown in the figure, a diversitycombiner 608 the input of which comprises a signal from the receiverunits, a decoder 610 to the input of which a signal that is visible atthe output of the diversity combiner 608 is connected, and control means612. The L digital complex I,Q samples 514 arriving from the antennaarray are supplied to the input of all the digital receiver units 600,602 and searcher units 604. If the arrangement according to theinvention is applied in a transmitter-receiver, the transmitter-receiveraccording to the invention also comprises an encoder 614 and a digitaltransmission unit 606.

The operation of the digital searcher unit 604 is examined first withreference to FIG. 6a. In the same way as in a conventional rakereceiver, the function of the searcher unit is to search for the desiredsignal components from the received signal. In the arrangement accordingto the invention, a new type of searcher unit continuously monitors thereceived signal in the (α, τ) domain and searches for useful signalcomponents and gives their parameters, i.e., the angle of arrival (AoA)and the delay profile, to the control means 612, which in turn allocatea required number of receiver units for demodulating the bestcomponents. The receiver according to the invention can naturally alsobe implemented such that a channel element does not comprise separatecontrol means 612, but the searcher unit 604 forwards the informationconcerning the signal components to be monitored directly to thereceiver branches 600, 602.

The searcher unit comprises means 634 for phasing the signal suppliedfrom the radio-frequency parts of the antenna array, and means 636 fordetecting whether the signal obtained from the output of the phasingmeans 634 comprises a signal component received with the given delay andfor measuring the quality of this signal component. The searcher unitfurther comprises means 638 for controlling the aforementioned phasingmeans 634 and the measuring means 636 such that the incoming directionsand delays of the received signal can be measured.

The means 634 for phasing the signal supplied from the radio-frequencyparts of the antenna array can be implemented, for example, withequipment of the type described above and shown in FIG. 4, the equipmentcomprising-the multiplication of the signal with complex coefficients w₁(i=1, . . . ,) by which it is possible to determine the angle of arrivalof the signal that is visible amplified in the output signal of thephasing means. Each combination of the coefficients corresponds to acertain combination of antenna beams, as described above. The phasingmeans (634) are controlled by the means 638 so that all the essentialincoming directions of the signal can be examined.

The output of the phasing means thus shows a signal that corresponds tothe signal received from a given direction on the basis of the controlof the means 638. The measuring means 636 perform a measurement withdifferent delays on a signal visible at the output of the phasing means,the purpose of the measurement being to detect the signal componentsthat have different delays. The delay to be measured each time is setwith the aforementioned means 638. In the measuring means, the signalsituated at the input of the means is subjected to despreading,measurement of the complex signal energy, and squaring of the energy,for example, over the coherence time of the channel, and comparison ofthe obtained measurement result with the given threshold value. Theparameters of the measured signal components having a strength exceedingthe given threshold value, i.e., the angle of arrival, delay and power,are provided to the control means 612 of the channel element.

The means 638 thus control the operation of the phasing means 634 andthe measuring means. The means 638 correspond to a synchronization loopprovided in the searcher branch of a conventional rake receiver, eventhough in the arrangement according to the invention the means operatein a new manner. The search for the desired signal components from the(α, τ) domain can be implemented in many ways under the control of themeans 638. As stated above, the measurement of the signal power can bereplaced with some other measurement of the signal quality.

The digitized signal received by the antenna array can be phased in thephasing means 634 step by step in such a way that the direction angle ofthe greatest gain is changed with given angle intervals. From among thepossible incoming directions, one selects a representative group ofangles of arrival ai which are situated at desired angle intervals fromone another, and each incoming direction is subjected to several energymeasurements at different delay values, whereby a delay profile τ_(k) isobtained for the incoming directions.

Another way is to direct the measuring means 636 to first measure thedelay profile τ_(k) of the received signal for example with anon-directional antenna pattern. The possible delays with which signalcomponents are received are thus detected. The phasing means 634 arethereafter directed to sweep the different direction angles with anarrow directional beam, and the measuring means are simultaneouslyguided to measure with the aforementioned delay values detected in thefirst measurement. The incoming directions α_(j) of the components thathave arrived with different delays are thus obtained.

The parameters of the detected signal components are thus given to thecontrol means 612 of the channel element. The control means allocate thereceiver elements 600, 602 to receive and demodulate the best detectedsignal components by informing the receiver element of the incomingdirection and delay of the signal component. As stated above, thereceiver elements can also be controlled directly by the searcher unit604 without separate control means.

The operation of the digital receiver unit 600, 602 will be examinednext with reference to FIG. 6a. In the same way as in a conventionalrake receiver, the function of the receiver unit is to receive anddemodulate a given signal component. Assume that the control means 612of the channel element have allocated a receiver unit to receive aparticular signal component the parameters of which are the angle ofarrival α_(j) and the delay τ_(k). The receiver unit 600, 602 comprisesmonitoring means 624, 632 to which the control means 612 of the channelelement forward the information about the phase and incoming directionof the signal component to be monitored. The monitoring means controlthe first phasing means of the receiver unit the input of which is thedigitized signal obtained from the antenna array. The phasing means 618,626 have a similar structure as the phasing means 634 provided in thesearcher unit. On the basis of the information that concerns the angleof arrival α_(j) and that is received from the control unit, themonitoring means set the complex weighting coefficients w_(i) (i=1, . .. ,L) such that a signal arriving from the desired incoming direction isvisible at the output of the phasing means. This can thus be understoodas a receiver antenna beam pointing in the desired direction and havinga predetermined shape.

The receiver unit 600, 602 further comprises demodulation means 620, 628the input of which comprises a signal obtained from the phasing means618, 626. The monitoring means 624, 632 guide the demodulation means tosynchronize with a signal component arriving with a given delay τ_(k).In the demodulation means, the signal is subjected to despreading anddemodulation according to known technology using the given τ_(k) as thecode phase. The obtained symbols are supplied to the other parts of thechannel element together with the delay data.

The receiver unit 600, 602 further comprises second phasing means 622,630 the input of which comprises a digitized signal obtained from theantenna array. The output signal of the second phasing means is suppliedto the monitoring means 624, 632. The monitoring means control theoperation of the second phasing means by measuring with the means theenvironment of the current parameters (α_(j), τ_(k)) of the signalcomponent allocated to the receiver in order to detect possible changesin the incoming direction and delay of the received signal component.For this purpose, the second phasing means comprise complex coefficientssimilar to the first phasing means for phasing the signal, and meanssimilar to the measuring means 636 situated in the searcher unit formeasuring the impulse response. If the monitoring means detect, by meansof the second phasing means, changes in the incoming direction α_(j) ordelay τ_(k) of the desired signal component, they update this data tothe first phasing means and to the demodulation means.

The prior art discloses several manners in which the monitoring means624, 632 can be implemented in a spread spectrum system, for exampleEarly-Late gates that can be used in the arrangement according to theinvention. These circuits estimate the code timing error by performingtwo energy measurements with the given time difference ΔT, which istypically a fraction of the chip time of the spreading code in theenvironment of the current set point τ_(k). The energy measurements areperformed with the measuring means of the second phasing means 622, 630,which provide the correction data required by the nominal set pointτ_(k) as the delay changes.

Correspondingly, changes in the angle of arrival α_(j) of the signal canbe monitored by means of the second phasing means. It is, for example,possible to perform, with the given delay Ski two or more energymeasurements with antenna beams which have been deflected by an angle Δαin both directions from the current angle of arrival α_(j) by means ofphasing. The degree of the deflection Δα used is typically a fraction ofthe width of the antenna beam.

The monitoring means 624, 632 thus control the energy measurementsperformed by the second phasing means 622, 630, so that a signal couldbe received with the greatest possible energy at all times. Themonitoring means update the data about the changed parameters (α_(j),τ_(k)) to the first phasing means, to the demodulation means and also tothe control means 612 of the channel element, so that the data could beused in the transmission direction, if required.

The above-described maximization of the received signal can be comparedwith the receiver antenna diversity used in conventional systems,wherein a signal is received with two or more antennas situated fromeach other at a distance having the length of several wavelengths of thereceived signal. In the receiver according to the invention, if a signalreceived with the angle of arrival α_(j) is caught in a deep and longfading situation, the fading can probably be eliminated by changing theangle of the receiver beam by a small angle Δα. There is thus no needfor two separate antennas situated at a given distance from each other.

The operation of the diversity combiner 608 and the decoder 610 of thechannel element is similar as in the prior art diversity receivers. Thecombiner 608 combines the symbol sequences arriving from the differentreceiver elements by taking into account and compensating for theirdifferent delays τ_(k) and possibly by weighting the different symbolsequences according to their signal-to-noise ratios in order to obtainmaximum ratio combination. The combined symbol sequence thus obtained issupplied to the decoder 610, which decodes the symbols to user databits, usually performing the deinterleaving first. The CDMA applicationsgenerally use a strong convolutional coding for which the best method ofdetection is the Viterbi algorithm providing a soft decision.

It is clear that the above-described channel element can also be usedfor monitoring and receiving an access channel. The antenna beams usedin the direction of reception have then wider antenna patterns, i.e.,they can be for example 120° wide, since the exact location of themobile stations transmitting call-set-up messages is not known.

The operation of the digital transmission unit 606 will be examined nextwith reference to FIG. 6a. The user data bits are first supplied to theencoder 614, which encodes the bits typically with a convolutional codeand performs interleaving on the encoded symbols. The obtainedinterleaved symbols are applied to a spread spectrum modulator 642,which performs conventional modulation. All the above-describedfunctions can be performed according to known technology.

In the present invention, the transmission unit comprises means 644,640, however, for controlling and phasing digitally the signal to betransmitted in response to the received signal. In the transmission unitaccording to the invention, the means 644 for adjusting the transmissionbeam receive from the control means 612 of the channel elementinformation in their input about the incoming directions used in thedifferent receiver units 600, 602 for receiving a signal from the mobilestation. The control means 612 may also report the other incomingdirections of the signal detected by the searcher unit 604, but not allthe directions are necessarily used in the reception of the signal.

The means 644 of the transmission unit for adjusting the transmissionbeam control the phasing means 640, which calculate from predeterminedbeam-forming functions J×L complex weighting coefficients w_(ij) (i=1, .. . L; j=1, . . . ,J) which produce J antenna beams by means of Lantenna elements. In addition to the direction and number of the antennabeams, the means 644 control the phasing means 640 by indicating thetransmit power that is to be used with each beam and that the means 644obtain from the control means 612 of the channel element.

The structure of the phasing means 640 may be similar to the phasingmeans 618, 626, 634 described above in the direction of reception. Inthe phasing means, the digitized (I,Q) samples of the outbound signalsupplied from the modulation means 642 are thus multiplied by L complexweighting coefficients where L is the number of the antenna elements, asfollows: ##EQU1## whereby L complex sample sequences are obtained forthe antenna array. The complex multiplication also uses a real scalingfactor g_(j) (j=1, . . . ,J), which is obtained from the adjusting means644 and which can be used for the independent power adjustment of eachantenna beam. The adjusting means 644 also indicate the frequency to beused, so that the weighting coefficients w_(ij) can be set correctly.

Examine next the embodiment of the invention according to FIG. 6b wherethe transmission unit according to the invention comprises means 648a to648b, 640a to 640b, 644 for controlling, delaying and phasing digitallythe signal to be transmitted in response to the received signal. In thetransmission unit according to the invention, the means 644 foradjusting the transmission beam receive from the control means 612 ofthe channel element information in their input about the incomingdirections and delays used in the different receiver units 600, 602 forreceiving a signal from the mobile station. The control means 612 mayalso report the other incoming directions and delays of the signaldetected by the searcher unit 604, but not all of them are necessarilyused in the reception of the signal.

The transmission unit thus comprises means 648a to 648b which transferon time domain each of the signals to be transmitted with a separatetime unit τ'_(j) (j=1, . . . ,J) determined by the control means 644, asdesired. The figure shows, by way of example, two means, but the numberof the means may naturally also be greater. Suitable values of the timeunits τ'_(j) may be derived for example from the delays of the signalcomponents of the signal received from the terminal equipment such thatthe terminal equipment receives the transmitted signal components withmutual time differences that exceed the length of the bit of thespreading code, i.e., the chip. Another alternative is to use the timeunits τ'_(j) to compensate for the mutual propagation delays in areaswhere the delay spread is great.

In order to enable delay control, the control means 612 of the channelunit transmit to the control means 644 information about the incomingdirection and delay of each detected signal component transmitted by aterminal equipment.

The transmission unit further comprises adding means 650 for combiningthe signal components that have different delays before thetransmission.

In the following, the arrangement of FIG. 6a will be discussed. Thearrangement according to the invention uses special beam control bitsthat a mobile station generates on the basis of the signal it hasreceived and that it adds to the signal it transmits to the basestation. The equipment according to the invention comprises means 616for demultiplexing and detecting these beam control bits from thereceived signal. The detection should be performed already before thedecoder 610 in order to avoid delays. The beam control bits areforwarded to the adjusting means 644 of the transmission unit.

The means 644 for adjusting the transmission beam control the phasingmeans 640 on the basis of the information obtained from the controlmeans of the channel element and the beam control bits transmitted bythe mobile station. The adjustment can be performed in many ways bymodifying the parameters α_(j) and g_(j) (j=1, . . . ,J) in differentways. For example the transmit power used with some antenna beams can beindependently adjusted, or the direction angle α_(j) of some antennabeams can be changed by a given angle Δα, or the number of the antennabeams used can be altered. With these measures it is possible tocompensate for the deteriorations of signal quality, such as fadings,occurring over the radio path.

In the arrangement according to the invention, the adjusting means 644of the transmission unit 606 can deflect the direction of one or severalof the used antenna beams by small degrees Δα in the environment of thegiven direction angle α_(j). Due to such deflection, it is possible toreduce the likelihood that the mobile station would be in a deep fadingfor a long time. Since the direction angle of an antenna beamcontinuously vibrates around a nominal direction angle α_(j), a signalthat has propagated over the radio path does not continuously use thesame route. This method can be considered a new type of antennadiversity in the downlink direction.

Further, in the arrangement according to the invention the adjustingmeans 644 can control the phasing means 640 such that a high-powersignal having a wide antenna beam is obtained from the antenna arraywith the suitable adjustment of the weighting coefficients w_(ij) (i=1,. . . ,L; j=1, . . . ,J) and the factors g_(j) (j=1, . . . ,J). Theobtained antenna pattern may be, for example, a sector pattern or anomnidirectional pattern. For example, a data-unmodulated pilot signalcan thus be transmitted with a permanent antenna pattern. The samemethod can also be applied in the transmission of control channels.

Also in the arrangement according to the invention, the adjusting means644 can control the phasing means 640 in such a way that with thesuitable adjustment of the weighting coefficients w_(ij) (i=1, . . . ,L;j=1, . . . ,J) and the factors g_(j) (j=1, . . . ,J), one or severalsignals having a rather narrow antenna beam are obtained from theantenna array, the angle of the greatest gain of the signal sweepingcontinuously the cell area. The obtained antenna pattern can be used forthe transmission of a data-unmodulated pilot signal.

The second preferred embodiment of the invention, wherein the analogphasing of a received signal and a signal to be transmitted is appliedin the CDMA system, will be described below.

FIG. 7 is a block diagram illustrating an example of the equipmentaccording to the second preferred embodiment of the invention. Theequipment comprises in the direction of reception a given number L ofantenna elements 700 to 704 and in the transmission direction a group ofantenna elements 772 to 776. In the transmitter-receiver, thetransmission and reception antennas may be the same, whereby duplexfiltration is used to separate the different transmission directionsfrom one another. The figure shows different antenna elements for thedifferent transmission directions. The group formed by the antennaelements may be linear, planar (two-dimensional) or omnidirectional. Theantenna array receives a multipath-propagated signal that is delayed indifferent ways from several different directions with each of the Lelements from each mobile station.

The antenna elements are connected to an RX matrix 706, which performsphasing on the analog signal received by the antenna elements such thatthe matrix output 708 comprises K signal outputs each of whichcorresponds to a signal received by an antenna beam pointing in apredetermined signal incoming direction. The matrix can be implementedby prior art arrangements, such as a Butler matrix that is realized withpassive 90° hybrids and phase shifters. The number K of the antennabeams produced with the matrix 706 does not necessarily correspond tothe number L of the antenna elements.

The antenna beams are thus obtained in the direction of reception byphasing the signal received by the antennas and in the transmissiondirection by phasing the signal to be transmitted by the antennas. Theantenna beams used are constant and their directions cannot be changed.The number of the antenna beams depends on the matrix 706 implementationand the beams can be set at desired angle intervals from one another andformed with a desired width.

The matrix output signals 708 are applied, if necessary, to a group oflow-noise amplifiers 710, which compensate for the cable attenuationsand other losses. The L signals amplified in this manner are supplied tothe radio-frequency parts 712 to 716, which subject each signal todown-conversion into an intermediate frequency and to the requiredfiltrations. The radio-frequency parts can be implemented in a manneraccording to known technology.

The intermediate-frequency signals are then applied to converter means718 to 722, which convert the analog signal into digital samples. Theconversion can be performed in manners according to known technologywith commercially available components. Typically, complex sampling intoI and Q components is performed in the means.

The output signals 724, 726, 728 of the converter means 718, 720, 722are supplied further to a group of channel elements 738, 740, 742 via anRX switch 732, 734, 730 preceding each channel element. All the outputsignals 730 of the converters are applied to all the RX switches. EachRX switch thus comprises K inputs and one or several output signals thatare applied to a corresponding channel element. The function of the RXswitch is to guide a signal received by a desired antenna beam to adesired component of the channel element according to control from thechannel element.

The above-described receiver structure can naturally also be implementedsuch that one or several of the aforementioned parts (antenna elements700-704, amplifiers 710, radio-frequency parts 712-716 and convertermeans 718-722) are located either integrated together or separately. Insuch a case, the details of the implementation vary, as it is evidentfor a person skilled in the art, for example, such a that if theradio-frequency parts are situated in connection with an antenna array,there is no need for amplifiers 710.

In the following, the structure and operation of a channel element in areceiver according to the second embodiment of the invention will bedescribed by means of the block diagram of FIG. 8a. The channel elementcomprises one or several means 804, 806, 808 for demodulating a signal,the figure showing three of the means, one or several searcher units 802one of which is shown in the figure, a diversity combiner 608 the inputof which comprises a signal from the receiver units, and a decoder 610to the input of which a signal visible at the output of the diversitycombiner 608 is connected.

The inputs In#1 to In#K of the RX switch 732 thus comprise the K signals730 from the converter means 718 to 722. The channel element 738 thuscomprises a searcher unit 802 the function of which is to perform thesearch for the best signal components from the multidimensional signaldomain, as described in connection with the searcher unit of the firstembodiment. In the present embodiment, the searcher unit 802 searchesfor the best signal components from the inputs of the RX switch, each ofwhich thus corresponds to a signal component arriving from a certaindirection, by measuring the delay profile from each input of the RXswitch. The measurement of the delay profile can be performed in thesame manner as in the searcher branch of a conventional rake receiver.As a result of the measurement, the searcher unit thus detects theincoming directions and delays of the best signal components. Thesearcher unit guides the demodulation means 804, 806, 808 to synchronizewith the best components by providing each demodulation means withinformation about the delay of the desired component and by applying thesignal of this direction from the RX switch to the correspondingdemodulation means.

The demodulation means 804, 806, 808 thus demodulate the given signal,monitor the changes in the delay and incoming direction of the signal,and start receiving a new antenna beam by means of the RX switch, ifrequired. The output signals of the demodulation means are applied to adiversity combiner 608, which preferably combines the demodulatedsymbols and detects the information transmitted. The output signal ofthe diversity combiner is applied further to decoding means 610, whichdeinterleave the symbols and decode the information sequence.

The above-described receiver structure thus implements the arrangementaccording to the invention by means of analog phasing. In the reception,a number (K) of fixed antenna beams are produced by the phasing, thestrongest signal components being selected for demodulation from thecomponents received by the antenna beams. As the terminal equipmentmoves and the incoming directions of the signal change, the signal ofthe antenna beam providing the best signal strength is always selectedfor demodulation.

The transmitter structure according to the second preferred embodimentof the invention will be examined below with reference to FIG. 8a.

The user data bits are first supplied to an encoder 614, which encodesthe bits typically with a convolutional code and performs interleavingon the encoded symbols. The obtained interleaved symbols are applied toa spread-spectrum modulator 642, which performs conventional modulation.All the above-described functions can be performed according to knowntechnology.

In the present invention, the transmitter implementation furthercomprises means 802 for controlling the analog phasing of the signal tobe transmitted in response to the received signal. Based on measurementsperformed, the searcher unit 802 knows the direction angles and thecorresponding antenna beams which receive the best signal components.The searcher unit allocates a group of demodulation means to receivethese components. In a practical implementation, the control of thetransmitting end can take place in the searcher unit or in a separatecontrol unit. For the sake of simplicity, only the first alternative isdescribed herein, without limiting the invention thereto, however. Inany case, the idea of the invention is the same in both alternatives. Asdescribed above, in the arrangement according to the invention thedetected incoming directions comprising a good signal level are usedwhen transmitting a signal to the opposite transmission direction.

The implementation of the transmitter part will be examined below bymeans of FIG. 7. The transmitter comprises a given number L of antennaelements 772, 774, 776, which may thus be the same as the antennaelements in the direction of reception. The antenna elements areconnected to a TX matrix 770 the function of which is to analogicallyphase the signal to be transmitted to different antenna elements so thatthe main beam of the directivity pattern points in the desireddirection. The input of the TX matrix comprises K signals 756, whichhave been converted into analog form in D/A converters 758 to 762,converted into a radio frequency and amplified in radio-frequency parts764 to 768. As already mentioned in connection with the description ofthe receiving end, the above-described components can be implemented inpractice in several ways either together or separately, as it is clearfor a person skilled in the art.

The TX matrix phases the K signals situated at the input in such a waythat the antennas provide antenna beams to K different directions, thedirections of the antenna beams being fixed and the beams coveringtogether the desired area. The implementation of the TX matrix 770 issimilar to the RX matrix 706 and it can be realized for example with aButler matrix that is implemented with passive 900 hybrids and phaseshifters. The number K of the antenna beams produced with the matrix 770does not necessarily correspond to the number L of the antenna elements.

The modulated data signal and the control 746 from the searcher unit aresupplied from each channel element 738, 740, 742 to the TX switchingmatrix 744, from which the signals are supplied further to adding means754. The operation of the switching matrix 744 and the adding means 754will be examined in greater detail by means of FIG. 9.

The TX switching matrix comprises a TX switch 900, 902, 904corresponding to each channel unit, the input of the switches consistingof both the modulated data signal that is to be transmitted and thatarrives from the channel unit, and a control signal 746, 748, 750 fromthe searcher unit of the channel unit. The output of the TX switchcomprises K outputs 746a to 746i, i.e., as many as there aretransmission antenna beams. The function of each TX switch is to routethe signal from the channel element to the correct transmission beams tobe summed together with signals arriving from the other channel elementsand intended to the same beam on the basis of the control from thechannel element. The TX switch guides the incoming data signal into oneor several outputs Txout#1 to Txout#K, depending on the control from thechannel element, i.e. depending on which antenna beams the signal isintended for. Each output is a quadratic digital sample weighted withthe signal level.

Each output 746a to 746i of the switch is applied to one of the K adders906 to 910 of the adding means 745. Each adder adds digitally togetherthe data signals arriving from different channel units and intended fora given antenna beam. The required bit number for an outbound sample isobtained with the formula 2*(log(n)+m), wherein n is the number of theinputs (channel units) of the adders, log is a two-based logarithm and mis the bit number of the samples.

Each of the outputs 756a to 756c of the TX switches is applied to acorresponding converter means 758 to 762 and further to antennas via ananalog phasing matrix, as described above.

An alternative transmitter arrangement according to the second preferredembodiment of the invention will be examined below with reference toFIG. 8b. A signal from the modulation means 642 is supplied to two ormore delay means 648a to 648b where the signals to be transmitted aredelayed with mutually different delays under the control of the searchermeans 802, whereupon the subscriber equipment can use diversity, asdescribed above, when receiving the transmitted signal.

As FIG. 7 illustrates, the signals 746 and 782, 748 and 780, and 750 and778 that have been delayed in different ways are applied from eachchannel element 738, 740, 742 to the TX matrix 744, the operation of thetransmitter after the TX matrix being similar to what has already beendescribed above.

The second preferred embodiment of the invention utilizes special beamcontrol bits, which a mobile station generates on the basis of thesignal that it has received and that it adds to the signal it transmitsto the base station. With reference to FIG. 8a, the receiver accordingto the invention comprises means 616 for demultiplexing and detectingthese beam control bits from the received signal. The detection shouldbe performed already before the decoder 610 in order to avoid delays.These beam control bits are forwarded to the searcher unit 802 of thechannel unit.

The searcher unit 802 selects the antenna beams to be used in thetransmission based on the information it has measured and the beamcontrol bits transmitted by the mobile station.

In the second preferred embodiment of the invention, a pilot signalsweeping the cell area in the form of a narrow antenna beam can beimplemented in such a way that the antenna beam used in the transmissionof the pilot signal is changed so that the pilot signal is transmittedby using each antenna beam in turn, whereby the pilot signal sweeps thecell area in stages.

Even though the invention is described above with reference to theexamples according to the accompanying drawings, it is clear that theinvention is not restricted thereto, but it can be modified in many wayswithin the scope of the inventive idea disclosed in the appended claims.

The alignment of the antenna beams can be used for example in both thevertical and the horizontal direction, whereby the above-described (α,τ) domain can be understood as an (α, β, τ) domain, wherein α is thevertical angle, β is the horizontal angle and τ is the delay.

One possibility is to utilize coherent, incoherent or differentiallycoherent modulation and demodulation methods in the channel elements.For example in order to enable coherent demodulation in a mobilestation, the base station may include an additional spreading-codedsignal without data modulation in each antenna beam as a phasereference. Alternatively, known reference symbols can be used for thesame purpose.

One alternative embodiment of the invention includes positioning thedigital phasing means 618 to 634 of the channel elements in one commonphasing means block, which services all channel elements.

What is claimed is:
 1. A base station equipment for receiving andtransmitting a signal of a desired user, said signal to be received mayarrive at said equipment along a plurality of paths with a plurality ofdelays, said equipment comprising:at least one antenna array comprisinga plurality of elements and at least one channel unit, said channel unitincluding means for phasing said signal to be transmitted and receivedby said antenna array such that gain from said antenna array is greatestin a desired direction, means for searching for incoming directions anddelays of said received signal components, and means for controllingsaid phasing means of an opposite transmission direction based on thereceived information.
 2. The base station equipment according to claim1, further comprising:a plurality of radio-frequency units coupled tosaid antenna array, wherein an input to said at least one channel unitincludes a signal from said radio-frequency units, wherein said channelunit includes at least one means for phasing said signal received bysaid antenna array such that gain obtained from said antenna array isgreatest in a desired direction, at least one means for demodulating adesired received signal component, wherein an input of said demodulationmeans is an output signal of said phasing means, means for searching forincoming directions and delays of said received signal components, andmeans for controlling said phasing means and said demodulation meansbased on said received information.
 3. The base station equipmentaccording to claim 2, wherein each said channel unit includes a controlunit regulating operation of said channel unit, at least one receiverblock, at least one searcher block, wherein an input of said blocksincludes a signal from said radio-frequency units, a diversity combinerwherein an input of said diversity combiner includes signals from saidreceiver blocks, and means for decoding said combined signal.
 4. Thebase station equipment according to claim 3, wherein said searcher blockincludes a phasing means, wherein an input of said phasing means is asignal from said radio-frequency units, means for detecting whether asignal received from a certain incoming direction and obtained from saidphasing means includes a desired signal component having a certain delayand for measuring a quality of said signal component, means forcontrolling said phasing means and said measuring means such that saidsignal to be received can be measured, and means for informing saidcontrol unit of said channel element of said incoming direction, delayand quality of each detected signal component.
 5. The base stationequipment according to claim 3, wherein said transmitter block includesa modulation means, wherein an input of said modulation means is asignal from an encoding means, said phasing means wherein an input ofsaid phasing means is a signal visible at an output of said modulationmeans, and means for controlling said phasing means such that saidgreatest gain of the signal to be transmitted can be oriented in saiddesired direction.
 6. The base station equipment according to claim 3,wherein said transmitter block includes a modulation means, wherein aninput of said modulation means is a signal from an encoding means fordelaying said signal components to be transmitted with desired timeunits and wherein an output of said encoding means being a signalvisible at an output of said modulation means, a phasing means coupledto said output of said encoding means, means for combining said signalcomponents having different delays before transmission, and means forcontrolling said phasing means and said encoding means such that saidgreatest gain of said signal to be transmitted can be oriented in saiddesired directions with the desired delays.
 7. The base stationequipment according to claim 1, wherein said phasing means includesmeans for multiplying said signal component received with each antennaelement by a complex weighting coefficient specifically set for eachsaid signal component, said coefficients guiding an angle of saidgreatest gain of a predetermined amplification pattern in said desireddirection.
 8. The base station equipment according to claim 1, furthercomprising:first means coupled to said antenna array for analogicallyphasing said received signal such that gain from said antenna array isgreatest in said desired beam-like directions; a first plurality ofradio-frequency units, wherein an input of said first plurality of radiofrequency units includes a phased signal; means coupled to an output ofsaid first plurality of radio-frequency units for digitizing saidsignal; at least one channel unit, wherein an input of said at least onechannel unit includes a digitized signal, said channel unit including atleast one measuring and switching means for searching for antenna beamscorresponding to said incoming directions of said received signalcomponents and for measuring delays of said components; and means fordirecting a best of said components to a demodulation means of saidchannel unit.
 9. The base station equipment according to claim 8,further comprising:second means coupled to inputs of said antenna arrayfor analogically phasing said signal to be transmitted with said antennaarray such that gain from said antenna array is greatest in said desiredbeam-like directions; a second plurality of radio-frequency unitscoupled to said input of said phasing means wherein, said input of saidsecond plurality of radio frequency units includes an output signal ofthe signal digitizing means; means for connecting said signal to betransmitted and obtained from each channel element to said desiredantenna beams based on control from said channel element; and meanscoupled to an output of a switching means for adding together signalsintended to the same antenna beam, an output of said switching meansbeing connected to said input of said digitizing means.
 10. The basestation equipment according to claim 9, further comprising:means fordelaying said signal components to be transmitted with desired timeunits.
 11. The base station equipment according to claim 9, wherein saidanalog phasing means includes a plurality of outputs, each said outputshows a signal received by an antenna beam pointing in a certaindirection.
 12. The base station equipment according to claim 7, whereina switching means guides said desired signals from digitized outputs ofan analog phasing means that have been converted into an intermediatefrequency and that are visible in said input of said switching means toa desired demodulation means under control of a measuring means, andwherein said measuring means guides each said demodulation means tosynchronize itself with said signal guided thereto.
 13. The base stationequipment according to claim 7, wherein said receiver includes means foramplifying said phased signal before digitizing.
 14. The base stationequipment according to claim 7, wherein said phasing means,radio-frequency units, and a converter means are positioned physicallyin the same unit.
 15. A method for steering an antenna beam in a basestation equipment in which a signal is received and transmitted by anantenna array by phasing said signal to be received and transmitted suchthat gain from said antenna array is greatest in a desired direction,said antenna array including a plurality of elements, said methodcomprising:in said base station equipment, searching for incomingdirections and delays of signal components received from a mobilestation; and controlling phasing of said signal to be transmitted in anopposite transmission direction based on the search.
 16. The methodaccording to claim 15, further comprising:phasing a received digitizedsignal such that gain from said antenna array is greatest in saiddesired direction; and controlling phasing and a phase of a demodulationmeans based on said search.
 17. The method according to claim 16,further comprising:measuring said incoming directions and delays of saidsignal components from said received signal by phasing said receiveddigitized signal step by step such that gain from said antenna array isgreatest in said desired incoming direction with a given angle interval;and measuring strength of said signal component in each incomingdirection with different phases of a spreading code.
 18. The methodaccording to claim 16, further comprising:phasing said signal to betransmitted, wherein an angle of greatest gain of a predeterminedamplification pattern points in said desired directions, and whereinsaid signal to be transmitted is delayed with desired time units. 19.The method according to claim 16, further comprising:analogicallyphasing said signal received by said antenna array such that gain fromsaid antenna array is greatest in desired beam-like directions; andguiding said desired signal components by a switching means to saiddemodulation means, wherein said phased signals are digitized, whereinsaid phased signal are measured from said received signal from antennabeams receiving best signal components, wherein delays of said bestsignal components are measured, and wherein said demodulation meanssynchronizes with said desired signal components.
 20. The methodaccording to claim 19, further comprising:analogically phasing saidsignal to be transmitted such that gain from said antenna array isgreatest in said desired beam-like directions; and guiding said signalto be transmitted by said switching means and an adder to a phasingmeans to be transmitted in said desired directions.
 21. The methodaccording to claim 19, wherein said received signal to be transmitted isphased analogically to provide a plurality of antenna beams pointing incertain directions.
 22. A base station equipment for receiving andtransmitting a signal of a desired user, said signal to be received mayarrive at said equipment along a plurality of paths with a plurality ofdelays, said equipment comprising:at least one antenna array comprisinga plurality of elements and at least one channel unit, said channel unitincluding a phaser for phasing said signal to be transmitted andreceived by said antenna array such that gain from said antenna array isgreatest in a desired direction, a searcher for searching for incomingdirections and delays of said received signal components, and acontroller for controlling said phaser of an opposite transmissiondirection based on the received information.
 23. The base stationequipment according to claim 22, further comprising:a plurality ofradio-frequency units coupled to said antenna array, wherein an input tosaid at least one channel unit includes a signal from saidradio-frequency units, wherein said channel unit includes at least onephaser for phasing said signal received by said antenna array such thatgain obtained from said antenna array is greatest in a desireddirection, at least one demodulator for demodulating a desired receivedsignal component, wherein an input of said demodulator is an outputsignal of said phaser, said searcher for searching for incomingdirections and delays of said received signal components, and acontroller for controlling said phaser and said demodulatorbased on saidinformation.
 24. The base station equipment according to claim 23,wherein each said channel unit includes a control unit regulatingoperation of said channel unit, at least one receiver block, at leastone searcher block, wherein an input of said blocks includes a signalfrom said radio-frequency units , a diversity combiner, wherein an inputof said diversity combiner includes signals from said receiver blocks,and a decoder for decoding the combined signal.
 25. The base stationequipment according to claim 24, wherein said searcher block includes aphaser, wherein an input of said phaser is a signal from saidradio-frequency units, a detector for detecting whether a signalreceived from a certain incoming direction and obtained from said phaserincludes a desired signal component having a certain delay and formeasuring a quality of said signal component, a controller forcontrolling said phaser and said measurer such that said signal to bereceived can be measured, and a notifier for informing said control unitof said channel element of said incoming direction, delay and quality ofeach detected signal component.
 26. The base station equipment accordingto claim 24, wherein said transmitter block includes a modulator,wherein an input of said modulator is a signal from an encoder, saidphaser, wherein an input of said phaser is a signal visible at an outputof said modulator, and a controller for controlling said phaser suchthat said greatest gain of the signal to be transmitted can be orientedin said desired direction.
 27. The base station equipment according toclaim 24, wherein said transmitter block includes a modulator, whereinan input of said modulator is a signal from an encoder for delaying saidsignal components to be transmitted with desired time units and whereinan output of said encoder being a signal visible at an output of saidmodulator, a phaser coupled to said output of said encoder, a combinerfor combining said signal components having different delays beforetransmission, and a controller for controlling said phaser and saidencoder such that said greatest gain of said signal to be transmittedcan be oriented in said desired directions with desired delays.
 28. Thebase station equipment according to claim 22, wherein said phaserincludes a multiplier for multiplying said signal component receivedwith each antenna element by a complex weighting coefficientspecifically set for each said signal component, said coefficientsguiding an angle of said greatest gain of a predetermined amplificationpattern in said desired direction.
 29. The base station equipmentaccording to claim 22, further comprising:first analog phaser coupled tosaid antenna array for analogically phasing said received signal suchthat gain from said antenna array is greatest in desired beam-likedirections; a first plurality of radio-frequency units, wherein an inputof said first plurality of radio frequency units includes a phasedsignal; digitizer coupled to an output of said first plurality ofradio-frequency units for digitizing said signal; at least one channelunit, wherein an input of said at least one channel unit includes adigitized signal, said channel unit including at least onemeasurer/switch for searching for antenna beams corresponding to saidincoming directions of said received signal components and for measuringdelays of said components; and a director for directing a best of saidcomponents to a demodulator of said channel unit.
 30. The base stationequipment according to claim 29, further comprising:second analog phasercoupled to inputs of said antenna array for analogically phasing saidsignal to be transmitted with said antenna array such that gain fromsaid antenna array is greatest in said desired beam-like directions; asecond plurality of radio-frequency units coupled to said input of saidphaser, wherein said input of said second plurality of radio frequencyunits includes an output signal of said digitizer; a connector forconnecting said signal to be transmitted and obtained from each channelelement to said desired antenna beams based on control from said channelelement; and an adder coupled to an output of a switch for addingtogether signals intended to the same antenna beam, an output of saidswitch being connected to said input of said digitizer.
 31. The basestation equipment according to claim 30, further comprising:a delayerfor delaying said signal components to be transmitted with desired timeunits.
 32. The base station equipment according to claim 30, whereinsaid second analog phaser includes a plurality of outputs, each saidoutput shows a signal received by an antenna beam pointing in a certaindirection.
 33. The base station equipment according to claim 28, whereina switch guides said desired signals from said digitized outputs of ananalog phaser that have been converted into an intermediate frequencyand that are visible in said input of said switch to a desireddemodulator under control of a measurer, and wherein said measurerguides each said demodulator to synchronize itself with said signalguided thereto.
 34. The base station equipment according to claim 28,wherein said receiver includes amplifier for amplifying said phasedsignal before said digitizing.
 35. The base station equipment accordingto claim 28, wherein said phaser, said radio-frequency units, and aconverter are positioned physically in the same unit.
 36. The methodaccording to claim 15, further comprising:phasing a received digitizedsignal such that gain from said antenna array is greatest in saiddesired direction; and controlling phasing and a phase of a demodulatorbased on said search.
 37. The method according to claim 36, furthercomprising:measuring said incoming directions and delays of said signalcomponents from said received signal by phasing said received digitizedsignal step by step such that gain from said antenna array is greatestin said desired incoming direction with a given angle interval; andmeasuring strength of said signal component in each incoming directionwith different phases of a spreading code.
 38. The method according toclaim 36, further comprising:phasing said signal to be transmitted,wherein an angle of greatest gain of a predetermined amplificationpattern points in said desired directions, and wherein said signal to betransmitted is delayed with desired time units.
 39. The method accordingto claim 36, further comprising:analogically phasing said signalreceived by said antenna array such that gain from said antenna array isgreatest in said desired beam-like directions; and guiding said desiredsignal components by a switch to said demodulator, wherein said phasedsignals are digitized, wherein said phased signal are measured from saidreceived signal from antenna beams receiving best signal components,wherein delays of said best signal components are measured, and whereinsaid demodulator synchronizes with said desired signal components. 40.The method according to claim 39, further comprising:analogicallyphasing said signal to be transmitted such that gain from said antennaarray is greatest in said desired beam-like directions; and guiding saidsignal to be transmitted by said switch and an adder to said phaser tobe transmitted in said desired directions.
 41. The method according toclaim 39, wherein said received signal to be transmitted is phasedanalogically to provide a plurality of antenna beams pointing in certaindirections.